1. Field of the Invention
The present invention relates to a calender arrangement for calendering a material web, in particular a paper web, having a shoe roll and a mating roll, between which an extended nip is formed, through which the material web can be guided. The shoe roll includes a revolving shell, which is fixed to two rotatably mounted terminating elements arranged at the ends and can be loaded in the direction of the mating roll via a press shoe matched to the outside of the mating roll.
2. Description of the Related Art
By using calender arrangements, material webs such as paper or board webs are calendered in order to obtain the desired surface quality. In this case, what are known as extended nip calenders in particular have proven worthwhile, in which the shell running over the press shoe of the shoe roll includes a relatively soft material, for example of polyurethane. The desired surface quality of the material webs is, in this case, achieved by applying pressure and heat by the mating roll normally being constructed as a heatable roll and the material webs guided through the extended nip being pressed in the direction of the heated mating roll via the press shoe.
As a result of the heating, the fibers of the material web are plasticized, which produces the desired surface smoothness and the desired gloss.
By way of the extended nip, as compared with calenders without an extended nip, a prolonged residence time in the nip is achieved, uniform compaction of the material web being ensured at the same time by the soft shell of the shoe roll.
However, in the known calender arrangements, it is a problem that the shells used are restricted to about 10 MPa with regard to the admissible compressive stresses, since otherwise the damage or destruction of a shell can follow. Furthermore, in connection with extended press shoes, there are problems in the formation of a pressure cushion for transmitting force.
What is needed in the art is a calender arrangement such that a compressive stress of up to 30 MPa can be transmitted without the shell being damaged or destroyed in the process.